1. Technical Field
The present invention relates in general to an improved method and system for providing a peripheral component interconnect (PCI) bus utilizing a flat cable. In particular, the present invention relates to an improved method and system for interconnecting PCI compatible printed circuit boards while allowing easy access to the surfaces of those circuit boards during testing and development. Still more particularly, the present invention relates to an improved method and system for providing access to PCI circuit boards during testing while simulating an electrical environment which is virtually identical to actual operating conditions.
2. Description of the Related Art
Modern computers utilize data buses to move data from one area of the computer to another. A modern computer has multiple data buses which interconnect different components of the computer system. Computer buses typically are implemented by a series of copper lines within a printed circuit board generally referred to as "traces."
A computer data bus is essentially a shared highway that interconnects different components of a computer system, including a microprocessor, disk-drive controller, memory, and input/output ports. Buses are characterized by the number of bits of data they can transfer at a single time (e.g., an 8-bit data bus simultaneously transfers 8 bits of data in parallel; a 16-bit data bus simultaneously transfers 16 bits in parallel). The bus is integral to internal data transfer. Bus (computer), Microsoft.RTM. Encarta.RTM. 96 Encyclopedia. .COPYRGT. 1993-1995 Microsoft Corporation. All rights reserved.
Modern personal computers have specialized data buses to maximize operational efficiency. High performance data buses within modern personal computers are specialized for interconnecting transaction intensive sub-systems. Generally, buses coupled directly to the main processor transfer data at a higher rate than peripheral buses. High speed buses require special design considerations to ensure system integrity.
Industry standards for bus architectures have been created by organizations within the computer industry. One such architecture which is gaining popularity is an architecture containing a "PCI bus." The PCI bus specification was derived from provisions introduced by Intel.RTM. Corporation. The Intel.RTM. provisions detail a local bus system for a personal computer. A PCI-compliant circuit cards can operate in a computer built to PCI standards. The PCI specification is continually being reviewed by computer industry committees such as the "PCI Special Interest Group."
An operational PCI local bus requires a PCI controller card to regulate bus utilization. Typically, the PCI controller card is installed in one of the PCI card receiving sockets. The PCI controller can exchange data with the computer's central processor, simultaneously transferring either 32 bits or 64 bits of data, depending on the implementation. A PCI controller additionally allows intelligent PCI-compliant adaptors to perform tasks concurrently with the CPU utilizing a technique called "bus mastering." The PCI specification also allows for multiplexing. Microsoft Press Computer Dictionary 295 (2ed. 1994).
Another bus standard is an industry standard bus. A PCI bus is a higher level or faster bus than the Industry Standard (ISA) bus. An ISA bus is typically utilized to interconnect a keyboard to the computer system, whereas a PCI bus typically interconnects devices requiring faster communication, such as disk drives and communication interfaces.
Due to the high data rate on a PCI bus, the physical interconnection of PCI-compliant circuit boards is critical. Transmission line properties such as interference susceptibility, impedance and length are critical to ensure bus communication integrity.
Computers built to PCI specifications can be upgraded or enhanced by adding PCI-compliant circuit cards. A PCI-compliant circuit board is often referred to as a "PCI card" by those skilled in the art.
Printed circuit boards which are sold to consumers generally have been subjected to extensive development and testing prior to their sale. The development phase of a printed circuit board can be very expensive. Design and production defects which avoid detection due to inadequate test capabilities can substantially add to the cost of a product. Production delays due to insufficient testing resources further add to the cost of a product.
A conventional personal computer contains a "motherboard" which provides internal buses to interconnect a main processor with other sub-systems of the computer. The motherboard is the main circuit board containing the primary components of the computer system.
A PCI circuit board undergoing a thorough development procedure must be electrically connected to an operational computer system. Due to the compactness of motherboards and rigid PCI bus specifications, PCI connectors are typically located close together on a motherboard. Visual access, as well as physical access to electrical signals during operation of PCI compatible circuit boards may be extremely limited.
Access to desired locations on a PCI circuit card during a test which utilizes a motherboard requires that the PCI card be remotely located from the motherboard. Testing typically requires an extension cable or an adaptor cable. For example, extension cables can be plugged into the motherboard and the PCI card, then the PCI card can be placed in a location which provides full access.
Alternately, special devices such as extender circuit boards can be plugged into a PCI card receiving socket to extend a duplicative connector at a location above surrounding PCI cards. An extender card places the board under test above surrounding obstructions and allow access to signals on the PCI card.
Often, initial PCI card design concepts are hand-wired by technicians. Typically, hand wired prototype circuit boards are physically much larger than allowed by the PCI specification. Hence, many conceptual designs will not fit in a conventional motherboard environment due to space constraints.
A commonly utilized development tool is a PCI extender card having right angle connectors. Extender cards with right angles provide access to signals on the top side of the PCI compatible circuit board, however, access to signals on the underside of the PCI card is again limited. Further, only one right angle extender card per system can be attached to the motherboard.
Generally, each party to the development of a PCI card has different requirements. Hence, a large quantity of application specific extender cards or test fixtures are built during the development of a product. Often, an application specific test fixture is useless after completion of the development of a specific PCI card.
Extender cards and test fixtures add to the cost of product development. Additionally, the added transmission line lengths introduced by adaptor cables and/or extender cards can create phenomena which is not present when the PCI card is plugged directly into a motherboard.
More particularly, card extenders or adaptors may degrade the signal quality on the PCI bus. Cables having excessive lengths induce data transfer problems, particularly timing skew and interference.
Currently, in the development of PCI compatible circuit boards, the circuit boards must operate in an electrical environment which is different from the electrical environment found in actual field operation. Often, not all of the design problems and difficulties can be determined utilizing extender cards and/or adaptor cables. Additionally, problems manifest in the development of PCI circuit cards which are a result of the test environment.
It therefore should be obvious that there is a need for a system and method for allowing access to the surface of a PCI compatible circuit board during operational testing. Further, a need exists for a reusable test fixture which accommodates oversized PCI compatible circuit boards. Additionally, it has become apparent that adequate testing of a PCI compatible card requires a test environment which accurately simulates field operating conditions.